Being confident of this very thing, that He who has begun a good work in you will complete it until the day of Christ Jesus.
— Philippians 1:6
Through Paul, Christ had begun a good work in the saints (1:6). Paul did not bribe any of them with promises of a better lifestyle if they stayed in the church life, nor did he threaten any of them that they would go to hell if they were to leave. Nothing besides Christ was mentioned.
The church in Philippi began after Paul had been imprisoned there (Acts 16). Paul and Silas were singing in jail, and then there was an earthquake, and everyone was released. The jailer was about to kill himself, but Paul and Silas intervened and he and his family were saved and baptized instead. There was no impure element involved; everything was just Christ. That was how the fellowship with the saints and the apostles and Christ began “from the first day.” Paul had the confidence to say that the Lord initiated this work, and He would also complete it.
Adapted from Oneness and the One Accord, pages 59-60.